Help: skin formation

Hi all,

When I leave my nicely formed baguettes in their floured couche, they proof nicely, however they form a really thick skin, even though I cover them with plastic wrap. Is this a normal occurence when proofing using a couce? I've only just started doing this :)

When it comes to baking them, it's really obvious when scoring the skin, and then the loaves don't seem to spring as much in the oven as I'd expect.

any ideas? I'm using the BBA formula.

thanks
JJ